Deposit types

Gold mineralization at the Marudi Property is regarded as being related to iron-formation-hosted gold (“IFG”) deposits that occur in other cratonic greenstone belts (e.g. Lupin, Musselwhite, in Canada, and Homestake in the western U.S.) These deposits can be remarkably long- lived with sizeable gold production (e.g. +/- 115 years, 65 M ozs Au). They have a strong association between gold and iron sulfide minerals, the presence of gold bearing quartz veins and structures, the occurrence of deposits in structurally complex terranes, and the lack of lead and zinc enrichment.

In stratiform IFG deposits much of the gold is uniformly disseminated in stratigraphically continuous horizons in well-laminated units of cherty, sulfide-rich BIF that are conformably interlayered with gold and sulfide poor BIF and clastic sedimentary rocks. Iron sulfide minerals are deformed and metamorphosed but oxide BIF is lacking. Late quartz veins or shear zones are volumetrically significant but their control on gold and iron-sulfide is unclear. Arsenic bearing minerals, if present are generally restricted to alteration zones immediately proximal to late quartz veins. World examples include Lupin, in Canada, Homestake in North Dakota (US), and Morro Vehho and Cuiabá in Brazil.

The strataform gold horizons at Marudi are genetically different from gold deposits and occurrences within the Guiana Shield in northern Guyana that have formed in structural (orogenic) belts in successive back-arc closure and extensional oceanic arc systems caused by migrating spreading ridges. These deposits form along convergent margins during terrane accretion, translation, or collision, related to plate subduction and/or lithospheric delamination. Brittle faults define conjugate patterns that are either trending north-northwest–south-southeast or north-northeast–south-southwest. Paleo-reconstructions indicate a similar pattern in West Africa. In West Africa the controlling structural trend is northeast-southwest. When compared at a regional scale, shear patterns of West Africa and those of the Guiana Shield appear to define a nearly conjugate pattern.

Paleo-Proterozoic reconstruction of the Guiana and West African shields. The Marudi Property is shown as a red triangle.